Multiple frequencies in the quantum oscillations of the superconductor YBa2Cu3O6.5

The discovery of de Haas-van Alphen oscillations, which are a thermodynamic probe of the density of states, in the underdoped high-temperature superconductor YBa2Cu3O6.5 demonstrated the existence of a well defined, close and coherent, Fermi surface in the pseudo-gap phase of these compounds [C. Jaudet et al., Phys. Rev. Lett. 100 187005 (2008)]. By improving the experimental conditions and extensive data accumulation, we have achieved very high precision magnetic torque measurements. The obtained results allow concluding that the oscillatory spectrum, so far believed to be composed of a single frequency, involve three main Fourier components with close values. This feature is attributed to bilayer splitting and warping of a single quasi-2D Fermi surface, confirming that c axis coherence is restored at low temperature in underdoped cuprates.

Figure: Left panel: YBa2Cu3O6.51 crystal glued to the cantilever beam for magnetic torque measurements. Right panel: dHvA data for YBa2Cu3O6.54 and YBa2Cu3O6.51.Solid lines are the best fits of the Lifshits-Kosevich model to the data including three Fourier components and harmonics. The observed beatings are nicely reproduced by the fittings.

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Multiple Quantum Oscillations in the de Haas-van Alphen Spectra of the Underdoped High-Temperature Superconductor YBa2Cu3O6.5.